Current induction



Aug. 14, 192s. 1,680,595

A. H. DAVIS, JR

CURRENT INDUCTION Filed Oct. 26, 1925 4 Sheets-Sheet l A. H. @AV/5, JR.

Aug. 14, 1928.

A. H. DAVIS, JR

CURRENT INDUCTION Filed oct. 26, 1925 4 Sheets-Sheet 2 Fuses Aug. 14,1928. 1,680,595

A. H. DAVIS, JR

CURRENT I NDUCT ION Filed Oct. 26, 1925 4 Sheets-Sheet 5 N NS Aug. 14,1928.

A. H. DAVIS, JR

CURRENT INDUCTION 4 Sheets-Sheet Filed opt. 26, 1925 ""lllllllll l1111/6511107" AHDAV/@Jm orzzeg Patented Aug. 14, 1928.

`UNITED STATES PATENT OFFICE.

ARCHIBALD H. DAVIS, JR., 0F BUFFALO, NEW YORK, ASSIGNOR T CHEMICAL CO.,INC., OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

CURRENT INDUCTION.

Application led October 26, 1925. Serial No. 64,806.

'This invention relates to the induction of currents and, in itsspecific application, to heating by induced currents.

Induced currents in a circuit vary with the number of lines of magneticiiux permeating the circuit; but the number of lines generated isdependent upon the mode of applying the current which causes themagnetic field. The usual arrangement of conductive elements in the formof'a solenoid results in a field of varying intensity with more lines offlux within the middle portion than at its ends. Consequently thesecondary electromotive forces vary, and the resulting induced currentsare modified accordingly. i

In addition, I have observed in connection with a solenoid, that theinduction of currents is affected by its conformation, or

shape, and by the arrangement of the conductive elements constitutingthe solenoid, that is, whether they are connected in series or inparallel or in combination of series and parallel. These effects may beattributed to leakages of flux lines being accentuated or increased bythe change in shape, and to the variations 'in counter electromotiveforces attendant upon the changes in the number of flux lines which areassociated with the conductive elements.

The variations of intensity in' the magnetic Held are of materialimportance in the application of induced currents for heating purposes,and the use of induced currents for heating a body, such as a vessel, isaccordingly made the basis for a disclosure of the invention. It is tobe understood, however, that the invention contemplates a wider field,including transformers and related structurcs` wherein secondarycurrents are `induced for purposes other than heating.r i

Inductional heating of vessels, such as kettles,'autoclaves and potsused in chemical processes, imposes requirements upon the conformationof the solenoid, on account of the variations in shape ofthe vessels,and the necessity for heat distribution and temperature control imposesothers as to the arrangement of the conducting elements and theirlocation relative to the vessel. Practical operation further'demands theuse of large currents with low losses, such as is offered by Iconductiveelements connected in para e.

This invention contemplates a compliance with these requirements, by aplacement of the conductive elements to generate a field with lines ofiux distributed to give the desired heating effect. As the best means ofdisclosing the nature of the invention, whereby this object isaccomplished, specific illustrations are given,

Restricting the consideration for the present to the effect of the shapeof the vessel and the resulting conformation of the solenoid, a specificapplication of the invention to a hemi-spherical kettle will bedescribed.

Such a kettle is not heated uniformly with a solenoid whose elementsform part of a conductor following the contour 'of the kettle and linkedtherewith through magnetic circuits of high reluctance, that is, whereair or other material of low magnetic permeability forms part of themagnetic circuit; but this condition is corrected by the application ofadditional coils in approximate proportion to the degree of decrease inthe slope. of the kettle wall.

In explanation of this corrective action, it may be advanced that thecurrents induced in the kettle walls become less as the slope decreases,that is, as the contour approaches the horizontal; or, that the lines oflinx, generated about the conductive elements and which permeate thekettle Wall, become less in number with the decrease in slope d ue tothe increased reluctance of the magnetic circuits linking the conductorswith the kettle walls. In order to have suiiicient'lines of flux followthe kettle wall, they must be deflected in part toward each other orconcentrated as the circular s ctional area, or the peripheralpathprovided for the secondary currents, decreases, and the repellentaction between them must be partially overcome. In other words, there isa disproportionate increased leakage of fiuX lines as the kettle -areadecreases, with induced electromotive forces decreasing at a, greaterrate than the resistances of the circuits for the secondary heatingcurrents. Additional ampere-turns of primary current is thereforerequired to set up the induced currents necessary for uniform heating,and coils added in approxi- 0 NATIONAL ANILINE mate proportions to thedecrease in slope give this result.

Another specific illustration, restricted to the effect of thearrangement of the conductive elements, in which there is no chan e fromthe straight cylindrical solenoid to a d complications, may also serveto elucidate the invention. It has been stated above that practicaloperation demands the use of conductive elements connected in parallel,but elements so connected are found to have most of the inducing currentcarried by the end elements and, as a result, they quickly becomeoverheated. This condition is corrected, and flow of current in all theparallel connected elements, is obtained by adding at an end of thesolenoid-like arrangement a few turns of a series coil which carries allthe current that is subdivided between the parallel connected elements.This coil is connected in series wit-h the parallel connected elementsand is in inductive relation with the end portion of the solenoidlikearrangement of the parallel connected coil. This arrangement equalizesimpedances by equalizing the magnetic field through all the coils. Sucha series coil is added at each end, unless the inductive elements arelocated about a portion only, such as the lower part, of the kettle. Inthe latter case, the mass of meta-1 in the kettle wall adjacent the endof the solenoid has a compensating effect thereon, and a smaller coilor, in some cases, none at all is needed at that end.

The explanation offered for the balancing effect of the series end coilsis that the iuX lines encircling the inductive elements at the end ofthe solenoid are relatively few in number, while they are relativelynumerous about the intermediate elements. The impedance in the end coilsis accordingly small and the current therefore flows principally inthem. With the addition of a series coil at a remote end in inductiverelation therewith, all the current is compelled to flow therethrough tocreate lines of flux proportionate to the number of turns. The result isthat additional flux is provided for the end elements to equalize thefield about the elements, and the current is then dividedproportionately among them. If the impedances of the elements connectedin parallel vary, due to differences in design and construction, thecurrent will be correspondingly divided among them and the heatingeffect modified accordingly.

In order to effect a control of the heating over a range oftemperatures, a plurality of groups of parallel-connected elements isprovided. When these groups are connected 1n series, a current of lowvalue passes through them and a low heat results. Connecting the groupsin parallel permits a heavy flow of current and consequently a highheat.

Either of these effects are modified by placing in circuit in series orparallel. With a plurahty of groups of parallel-connected elements, 1tbecomes necessary to add a series conductor only at a remote end of theassemblage, the adjacent ends of the groups havinga balancing effectsimilarly to the individual elements. The series conductor so added canbe made of overlapping elements if it is in proximity to a portion ofthe vessel where a change in the sectional. diameter occurs.

The invention is applicable for use with electrically conductive vesselsof magnetic or non-magnetic material. With the former, the hysteresiseffect is added to that of an eddy current effect common to both. Toprevent the unnecessary escape of heat, in sulationcan be placed aboutthe vessel and the conductive elements, or located between them. Meanswithin or without the insulating jacket can be provided for cooling theconductive elements or the vessel or both.

For a more complete understanding of the' invention, reference is to behad to the following description, and accompanying drawing, in whichFig. 1 is a vertical section of a kettle and acontinuous conductor aboutsaid kettle;

Fig. 2 is an enlarged detail of Fig. 1;

Fig. 3 is a wiring diagram therefor;

Fig. 4 is a vertical section of a round bottom kettle with a flat coilconductor associated therewith;

Fig. 5 isa vertical section of a kettle having flat induction coilsconnected in parallel and series and coils; and

Fig. 6 is a wiring diagram of the circuit incorporated in Fig. 5.

In the embodiment shown in Figs. 1, 2 and 3, an autoclave or vessel 1 iscarried by channel beams 2, supported on columns 3, and has verticalstraps 4 by which are carried `porcelain insulators 5. These insulatorssupport the conducting elements 6. The straps are connected at theirupper ends by a ring 7 and have inwardly inclined portions 8 supportinginsulators below the spherical bottom; and the portions 8 also carry anadditional row of insulators 9, so that the conducting elements aredoubled about the spherical portion. Enclosing the autoclave is a heatinsulating casing 10, covered by a shell 11 and supported from a channelring 12 carried by legs 13 to which the straps 4 are attached; and pushdoors 14 in the insulation give access to the interior. A bottom.insulation 15 is supported on a plate 16 that is bolted to the ring 12and has a sliding door 17 and removable insulation block 18.

In this installation the conducting elements form parts of onecontinuous conductor in two coils 19 and 20, one external of the other,and having leads 21 and 22 extending from the upper portion of theadditional conductors either casing. Included as part of the inside coil19 is a portion returning upon itself about the curved bottom, where theinsulators are doubled, and taking the place of the outside coil, Theoutside coil 2() is led through the outer row of insulators 9 andlikewise doubled upon itself. An intermediate tap 23 leads from amid-point of the outside conductor coil, and a lead 24 extends from theend of the inside coil. A tap 25 cuts out the portion of the outsidecoil passing through the insulators 9, and a lead 26 is the terminus ofthe outside coil. The con- Y trol of current in these various portionsof proportionately overlapped as shown.

the vcoils by means of switches is clearly illustrated in Fig. 3.

With this arrangement, the primary cur rent passses about the vesselthrough one coil, then in series through the four coils about thespherical botto-m and into the other cylindrical coil. The mid-point tappermits cutting the upper end of the outer coil out of the circuit, orit alonecan be in circuit; and' similarly the leads 24, 25 and and 26permit the use or cutting out of sec tions'of the coils about the lowerportion.

In the modified embodiment shown in Fig. 4, fiat vertical coils 27connected in series are used, each coil consisting of a number of turns.The coil is placed about a hemispherical kettle 28 and, as the diameterof a horizontal section decreases, th-e coils are In this form, heatinsulation 29 is placed between the kettle and the primary coils. Thekettle and the coils are carried by a frame `work 30; and-a casing 31encloses the coils.

Fi s. 5 and6 disclose another embodiment in W ich fiat coils connectedin parallel are used. A fusion pot 32 is carried by a frameworkconsisting of legs 33 and channel rings 34, 35, and the same frameworkcarries the fiat coils 36. Insulation 37 separates the coils and thekettle. A casing 38 encloses the coils and air circulation within thecasing is secured by a conduit 39, connecting a ventilation fan with abottom cone-shaped plate 40. A deflectirg cone 41 direct-s the airtoward the coils. The air passes between the coils and out at the lowerend of the casing 38.

The coils are connected in two groups, 42, 43, six coils being shown ineach group connectedv in parallel. In series with each group at theouter or remote end .is a coil 44 of four turns of heavy wire, and thereare also two half coils 45, 46 at the outer remote end of each group. Adouble throw switch 47 connects each group to the feed mains 48, so thatthe groups can be connected in series or in parallel; and a single' poleswitch 49 throws the upper half coils into or'out of circuit when thegroups of coils are connected in series.

lAll the current in this form of the appa` ratus passes to a groupthrough the heavy wire coil 44, While the current through the coils,comprising a group, is subdivided between the coils. When the doublepole switch 47 is down, the two groups are connected in parallel givingthe greatest current flow and the highest heat; when the switch isthrown up and the two groups are connected in series, there is a smallercurrent flow and a low heat is the consequence. Further reduction inheat is obtainable by connecting in series the upper two half coils bymeans of the single pole switch 49 thrown into the upward position. Thelower half coils 46 provide additional heat regulation and may beconnected in the circuit if found necessary.

While `the air circulation is disclosed by the embodiment illustrated inFigs. 5 and 6, it yis readily applicable to the other forms. With thearrangement of the irst embodiment the air, or other suitable coolingmedium, is passed within the insulated casing. In this case both t-hevessel and the coils are cooled.

From the preceding, it follows that the invention provides for adistribution of the magnetic field and the induced currents inaccordance with the heating effect desired. If a concentrated heat in aportion of the vessel or a uniform heat Jin a portion of variableformation is desired, the conductive elements are confined to orconcentrated about that portion, the elements being overlapped orassociated with a series conductor, depending upon the shape of thevessel and the wiring arrangement adopted. Whilethe series'conductorassocia-ting a group of parallel connected coils is shown concentratedat the end of the group, it can be of varying extent or connected with acontinuous conductor in combination with the parallel-connected group.-Where the group of parallelconnected coils extends onl of the vessel,for instance, t e lower end, the upper series coil may be of diminishedsize, or omitted, as the vessel wall extending beyond the coils has, toa greater or less extent, an eii'ect similar to that of a series endcoil on the iow of current through the parallel-connected coils.

The general application of the underlylng principles of this inventionto types of ap' paratus other than heating apparatus is clear.Accordingly the claims are not to be restricted to the specificembodiments, chosen to disclose the invention, but are to be given aninterpretation commensurate with the field covered by them; and by theterm body is to be understood a vessel or any arrangement, includingvcoils constituting closed circuits and particularly annularlikearrangements, where in secondary currents may be induced for utilitarianpur- I claim:

1. An electrical induction apparatus comprising in combination, anelectrically conductive body, and a plurality of current conductiveelements about said body, said elements being relatively more numerousabout a portion of the body.

2. An inductive heating apparatus comprising in combination anelectrically con-- ductiveJ vessel, said vessel having a contractedportion, and a plurality of current conductive elements about saidvessel, said elements being relatively more numerous about thecontracted portion of the vessel.

3. Electrical induction apparatus including in combination a body to beheated, current conductive elements for generating magnetic lines offlux permeating said body, and means in association with said elementsfor compensating Jfor leakage of flux with respect to said body, saidmeans comprising additional conductors adjacent to areas of magneticleakage.

ll. An inductive heating apparatus comprising in combination anelectrically conductive vessel, said vessel having a contraced portion,and a conductor in inductive relation with said vessel, said conductorbeing in. part concentrated about the conc tracted portion of thevessel.

5. An inductive heating apparatus comprising in combination anelectrically conductive vessel, said vessel having a portion varyinginsection, and a conductor having a plurality of turns about said vessel,said turns varying inversely in number in approximate ratio with thevariation in section.

6. An inductive heating apparatus comprising in combination anelectrically conductive vessel, said vessel having a portion ofdecreasing sectionaldiameter, and a conductor having a plurality ofturns about said vessel, said turns increasing in number in approximateratio with the decrease in the sectional diameter.

7. An electrical induction apparatus comprising an electricallyconductive body to be heated, a primary circuit composed of a pluralityof current conductive elements forming a coil encircling said body, saidelements being connected in parallel, and an additional currentconductive element encircling said body and connected in series to saidparallel connected elements, said additional element being in inductiverelation to an end section of said coil for regulating the relative flowof current in said parallel connected elements.

8. An electrical induction apparatus comprising an electricallyconductive body to be heated, a primary circuit composed of a pluralityof current conductive elements formin a coil encircling said body andlinked therewith through magnetic circuits of high and spacedreluctance, said elements being connected in parallel, and an additionalcurrent conductive element encircling said body and connected in seriesto said parallel connected elements, said additional clement being ininductive relation to an end section of said coil for regulating therelative flow of current in said parallel connected elements.

9. An inductive heating apparatus comprising in combination, anelectrically conductive vessel of varying diameter, conductive elementsin inductive relation with said vessel, said elements varying inverselyin concentration about the vessel according to its diameter, means forconnecting two or more of said elements in parallel, and meansassociated with the parallel connected elements for regulating therelative tlowof current in said parallel elements.

10. An inductive heating apparatus comprising in combinationv anelectrically conductive vessel, a conductor in inductive relationwith'said vessel, heat insulating means associated with said vessel, andcooling means therefor.

11. Electrical induction apparatus including in combination a body,current conductive elements for inducing currents in said body, andmeans in association with said elements for simultaneously regulatingthe distribution of the currents induced within said body.

12. Inductive heating apparatus including in combination a vessel,current conductive elements for inducing heating currents in saidvessel, andmeans in association with said elements for equalizing thedistribution of the currents induced within said vessel.

13. Electrical induction apparatus including in combination a body,current conductive elements for generating magnetic lines of fluxpermeating said body, and means in association with said elements forcompensating for leakage of flux with respect to said body.

14. Inductive heating apparatus comprising in combination a vessel andcurrent conductive elements about the vessel for inducing heatingcurrents in the vessel wall, said elements being arranged with relationto the vessel wall to regulate the distribution of the heating currents.

15. An inductive heating apparatus comprising in combination anelectrically conduct-ive vessel, a conductor in inductive relation withsaid body, heat insulating means positioned between said vessel and saidconductor, a casing enclosing said conductor therefrom and means forcirculating a iiuid cooling medium over said conductors.

16. Inductive heating apparatus including in combination a vessel to beheated, current. conductive elements for inducing heating currents insaid vessel, and means in association with said elements for equalizinthe distribution of the currents induce Within said vessel, said meanscomprising additional conductors adjacent to areas of diminishedsecondary current intensity.

17. An electrical heating apparatus comprising in combination anelectrically conductive vessel and a primary coil having a plurality ofconductive elements in inductive relation to the side walls ofvsaidvessel arranged more numerously about a portion of said walls so as toregulate the distribution of the currents induced within said vessel, amagnetic circuit surrounding said primary coil being provided by a wallportion of said vessel lon the inner side of the coil and the atmosphereadjacent the outer side of said coil;

18. An electrical heating system comprising an electrically conductivebody to be heated, a primary circuit for induclng currents in said bodycomposed of a plurality of current conductive elements arranged alongthe side surfaces of said body in nductive relation thereto, and asource of current for energizing said primary circuit, the ampere-turnsof said primary circuit being greater about a portion of said surfacesto regulate the distribution of the currents induced in said body.

. 19. An electrical heating system compris ing an electricallyconductive vessel to be heated, a primary circuit for inducing currentsin said vessel comprising a coil of current conductive elementsencircling said vessel and arranged along the side walls thereof, saidconductive elements being linked with said vessel through magneticcircuits of high reluctance, and a source of current for energizin saidprimary circuit, the ampere-turns o said primary circuit being greaterin an end portion of said coil than in a central portion of the coil, toregulate the distribution of currents induced in said vessel. i i

In testimony ,whereof I aiiix my signature.

ARCHIBALD H. DAVIS., Jn.

